Introduction Learning Objectives Flashcards
Discuss the importance of studying microbial/bacterial pathogenesis.
- Infectious diseases are a leading cause of death worldwide
- Healthcare associated infections (HAIs) are severe (can lead to sepsis or death) and also have a heavy financial burden on hospitals and society
What is the normal microbiota?
Microorganisms frequently found on or in the body of healthy persons
Define the three “internal” surfaces that are contiguous with the outside environment.
- Respiratory tract
- Upper: nose, nasal cavities, mouth, larynx, pharynx
- Lower: trachea, bronchial tree, lungs - Digestive tract: mouth to large intestine
- Genitourinary tract: anterior parts of urethra, vagina
Describe the anatomical locations for normal bacteria microbiota and list the frequent types at these locations.
- Skin: Staphylococcus, Corynebacterium, Propionibacterium acnes, Enteric bacilli
- Oropharynx: α-Hemolytic steptococci, Micrococcus, Corynebacterium, Neisseria, Haemophilus, Spirochetes
- Large intestine: Streptococccus (enterococci), Lactobacillus, Clostridium, Bacteriodes, enteric bacilli
- Vagina: Streptococcus, Lactobacillus, Bacteroides, Mycoplasma
What are the functions of the normal microbiota?
- Immune stimulation
- Keeping out invaders
- Human nutrition and metabolism
- Conversion of ingested compounds
Explain the three types of microbe-host interactions and give an example for each.
- Mutualism: relationship benefits both microbe and host (ex. most of the normal microbiota)
- Commensalism: relationship only benefits the microbe but the host isn’t harmed (ex. non-pathogenic E. coli in the intestinal tract)
- Parasitism: relationship benefits the microbe and harms the host, producing infection or disease (ex. viruses)
Define pathogen.
A microorganism capable of causing a disease
Define pathogenicity.
The ability of a microbial pathogen to infect its host and produce a disease
Define virulence.
The degree of pathogenicity
Define virulence factor.
Strategies that contribute to virulence
- Not associated with viability
Define opportunistic pathogen.
A microorganism that usual only causes infection in a damaged or
immunocompromised host
Describe the sources of opportunistic pathogens.
- Commensals when the host defense is compromised
- Commensals in different locations in the body
- Commensals that acquire pathogenicity
- Environmental microbes that are pathogenic to the immunocompromised
Compare and contrast infection and disease and define infectious disease.
- An infection is the establishment of a microbial pathogen while a disease is the clinical manifestation of damage to host cells and tissues (caused by the infection)
- Infectious disease: illnesses caused by infections
Define intoxication.
Disease caused by the ingestion of a preformed toxin without infection
Describe the 6 events in the establishment of a bacterial disease.
- Encounter: pathogen meets host
- Sources and transmission
- Exogenous infection
- Endogenous infection - Entry: pathogen enters host
- Preferred site of entry: tissue tropism
- Ingress vs. penetration - Spread: pathogen spreads from site of entry
- Dissemination - Multiplication: pathogen multiplies in host
- Threshold number to cause disease - Damage: by pathogen, host response, or both
- Outcome: pathogen or host wins or they coexist
Explain why the development of a bacterial disease may not involve all these six events.
Sometimes the outcome can occur earlier (not necessarily the sixth step), which then stops the development of the disease
List the three major reservoirs of infectious agents.
- Human reservoirs
- Animal reservoirs
- Nonliving reservoirs
Describe the two modes of transmission and assign a mode of transmission to each of the examples in Table 58.2.
- Direct transmission: infectious agent is transferred by direct contact (person to person, contact with soil/vegetation harboring infectious organisms)
- Indirect transmission: transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects (vehicles), or animate intermediaries (vectors)
Define zoonosis.
A disease of nonhuman animals. Many, but not all, zoonoses may cause disease in humans.
Define carrier of an infectious agent.
Organism carrying a pathogen but having no disease symptoms